For over a decade, forced-air warming (FAW), via an inflatable air blanket, has been used in operating rooms to prevent hypothermia in surgical patients. It is well established that surgical patients under anesthesia become poikilothermic. This means that the patients lose their ability to control their body temperature and will take on or lose heat depending on the temperature of the environment. Since modem operating rooms are all air conditioned to a relatively low temperature for surgeon comfort, the majority of patients undergoing general anesthesia will lose heat and become clinically hypothermic, if not warmed. FAW has become the “standard of care” for preventing and treating the hypothermia caused by anesthesia and surgery. FAW consists of a large heater/blower attached by a hose to an inflatable air blanket. The warm air is distributed over the patient within the chambers of the blanket and then is exhausted onto the patient through holes in the bottom surface of the blanket. Although FAW is clinically effective, it suffers from several problems including: a relatively high price; air blowing in the operating room, which can be noisy and can potentially contaminate the surgical field; and the inflatable blanket is relatively bulky over the patient, at times even obscuring the view of the surgeon. Moreover, the low specific heat of air and the rapid loss of heat from air requires that the temperature of the air, as it leaves the hose, be dangerously high—in some products as high as 45° C. This creates significant dangers for the patient. Second and third degree burns have occurred both because of contact between the hose and the patient's skin, and by blowing hot air directly from the hose onto the skin, without connecting a blanket to the hose. This condition is common enough to have its own name—“hosing.” The manufacturers of forced air warming equipment actively warn their users against hosing and the risks it poses to the patient.
The logistics of FAW and the bulk of the inflatable air blankets have motivated the development of electric or warm water circulating heating blankets. Many of these heating blankets are reusable so that the blankets must either be cleaned between uses, or the blankets must be enclosed in a clean cover for each use. Inadequate cleaning can cause cross contamination between patients. Cleaning is not only time consuming during the rapid turnover of the operating room after each case, but the labor for the cleaning is also expensive. Some reusable covers are formed with pockets having an open edge. This edge access point is ideal for inserting small, stiff heater cards or pads into small pockets. However, if the heater is flexible and is large, the size of a blanket, inserting it into a protective pocket from the side, is nearly impossible. There is a need for heating blanket covers that are easily manipulated for placing a heating blanket therein and do not compromise the comfort of a person over which the blanket is placed.